Pioneering work by Hisaw 1926 first suggested an important role for the peptide hormone relaxin in animals through its effect in dilating the pubic symphsis, thus facilitating the birth process. Relaxin is synthesised in the corpora lutea of ovaries during pregnancy, and is released into the blood stream prior to parturition. The availability of ovarian tissue has enabled the isolation and amino acid sequence determination of relaxin from the pig (James et al (1977), Nature, 267, 554-546), the rat (John et al (1981) Endocrinology, 108, 726-729), and the shark (Schwabe et al (1982) Ann. N.Y. Acad. Sci., 380, 6-12).
Relaxin genes and the encoded relaxin polypeptides have been identified in many species including man, pig, rat, sheep and shark. In all these species only one relaxin gene has been characterised in mammals, with the exception of the human and higher primates where two separate genes have been described. The separate human genes were identified by the present applicant and designated H1 (Hudson et al (1983) Nature, 301, 628-631) and H2 (Hudson et al (1984) Embo. J., 3, 2333-2339).
The peptide encoded by the H2 gene is the major stored and circulating form in the human (Winslow et al (1992) Endrocrinology, 130, 2660-2668). H1 relaxin expression is restricted to the decidua, placenta and prostate (Hansell et al (1991) J. Clin. Endocrinol. Metab., 72, 899-904), however, the H1 peptide has similar biological activity to that of H2 relaxin in a rat atrial bioassay (Tan et al (1998) Br. J. Pharmacol 123, 762-770).
The actions of relaxin include an ability to inhibit myometrial contractions, to stimulate remodelling of connective tissue and to induce softening of the tissues of the birth canal. Additionally, relaxin increases growth and differentiation of the mammary gland and nipple and induces the breakdown of collagen, one of the main components of connective tissue. Relaxin decreases collagen synthesis and increases the release of collagenases (Unemori et al (1990) J. Biol. Chem. 265, 10682-10685). These findings were recently confirmed by the establishment of the relaxin gene-knockout mouse (Zhao et al (1999) Endocrinology 140, 445-453), which exhibited a number of phenotypic properties associated with pregnancy. Female mice lacking a functionally active relaxin gene failed to relax and elongate the interpubic ligament of the pubic symphysis and could not suckle their pups, which in turn, died within 24 hours unless cross-fostered to relaxin wildtype or relaxin heterozygous foster mothers.
Evidence has accumulated to suggest that relaxin is more than a hormone of pregnancy and acts on cells and tissues other than those of the female reproductive system. Relaxin causes a widening of blood vessels (vasodilatation) in the kidney, mesocaecum, lung and peripheral vasculature, which leads to increased blood flow or perfusion rates in these tissues (Bani et al (1997) Gen. Pharmacol 28, 13-22). It also stimulates an increase in heart rate and coronary blood flow, and increases both glomerular filtration rate and renal plasma flow (Bani et al (1997) Gen. Pharmacol. 28, 13-22). The brain is another target tissue for relaxin where the peptide has been shown to bind to receptors (Osheroff et al (1991) Proc. Nal. Acad. Sci. U.S.A. 88, 6413-6417; Tan et al (1999) Br. J. Pharmacol 127, 91-98) in the circumventricular organs to affect blood pressure and drinking (Parry et al (1990) J Neurodendocrinol 2, 53-58; Summerlee et al (1998) Endocrinology 139, 2322-2328; Sinnahay et al (1999) Endocrinology 140, 5082-5086).
Important clinical uses arise for relaxin in various diseases responding to vasodilation, such as coronary artery disease, peripheral vascular disease, kidney disease associated with arteriosclerosis or other narrowing of kidney capillaries, or other capillaries narrowing in the body, such as in the eyes or in the peripheral digits, the mesocaecum, lung and peripheral vasculature.
The finding of two human relaxin genes, and encoded human relaxin peptide products nearly 20 years ago was of itself most surprising.
Even more surprisingly with the benefit of nearly 20 years of further research and development in relaxin biology internationally, the applicant has identified, isolated and characterised nucleic acid sequences encoding a third human relaxin gene (H3), the encoded H3 relaxin peptide and the constituent peptide chains thereof. The production of H3 relaxin and analogues thereof has been made possible, as have uses and therapeutic treatment methods.